I'm on another forum where someone stated that they were going to skip their first flight. The situation is thus:

Return MAN - DXB booked at UK prices.

MAN - DXB leg is 8th December, she is in DXB now so won't get on this flight.
DXB - MAN leg is mid December, she'll use this return as outward leg

MAN - DXB one way booked to get home.

She said she had been told by her travel agent that all it would cost is £80 for the "no show" on the first leg, surely thats not right?

I've said the whole itinerary will be cancelled if she doesn't show for the first flight from MAN-DXB. This happened to me some time ago when I was booking back-to-backs with a single at either end and made the mistake of not being able to make the first flight of one of the back-to-back returns.